Wide band transducer

ABSTRACT

A transducer assembly comprising one or more ring shaped transducer elements of a ceramic material which are rigidly held between a rear mass and a front mass, both of which are made to vibrate by energizing the ceramic material. Mounting rings and coupling necks having a distributed mechanical impedance are placed between the transducer elements and each of the masses. The entire assembly is held together by a tie rod which enters only a small distance into the front and rear masses. The mounting rings are located close to the nodal point of a mechanical resonance and are secured to an outer case by means of sound isolating material in a configuration wherein the sound isolating material experiences minimal vibrational excursions because of the near nodal mount. The compliance of the coupling necks and the compliance of the vibration isolating material is utilized in shaping the upper and lower portions of the frequency bandpass characteristic.

United States Patent Ehrlich et al.

1 Jan. 14, 1975 1 1 WIDE BAND TRANSDUCER [75] Inventors: Stanley L. Ehrlich, Middletown',

Anthony F. Medeiros, Portsmouth, both of RI.

[73] Assignee: Raytheon Company, Lexington,

Mass.

[22] Filed: June 1, 1973 [21] Appl. No.: 365,928

[52] US. Cl 340/10, 3l0/8.7, 340/12 [51] Int. Cl. H04b 13/00 [58] Field 01 Search 340/8, 9, 10, l2, l3, l4; 3l0/8.7

[5 6] References Cited UNITED STATES PATENTS 2,945,208 7/1960 Samsel 3l0/8.7 X 2,961,637 11/1960 Camp 340/9 3,230,503 1/1966 Elliot, Jr. et al. 340/10 3,337,844 8/1967 Baltakis 340/10 3,460,061 8/1969 Massa 3,474,403 10/1969 Massa et a1. 340/10 3,487,238 12/1969 Angleton et a1... 3l0/8.7 X 3,769,532 10/1973 Tocquet et a1 340/10 X Primary ExaminerBenjamin A. Borchelt Assistant ExaminerH. J. Tudor Attorney, Agent, or Firm- David M. Warren; Joseph D. Pannone; Milton D. Bartlett [57] ABSTRACT A transducer assembly comprising one or more ring shaped transducer elements of a ceramic material which are rigidly held between a rear mass and a front mass, both of which are made to vibrate by energizing the ceramic material. Mounting rings and coupling necks having a distributed mechanical impedance are placed between the transducer elements and each of the masses. The entire assembly is held together by a tie rod which enters only a small distance into the front and rear masses. The mounting rings are located close to the nodal point of a mechanical resonance and are secured to an outer case by means of sound isolating material in a configuration wherein the sound isolating material experiences minimal vibrational excursions because of the near nodal mount. The compliance of the coupling necks and the compliance of the vibration isolating material is utilized in shaping the upper and lower portions of the frequency bandpass characteristic.

3 Claims, 1 Drawing Figure WIDE BAND TRANSDUCER BACKGROUND OF THE INVENTION Sonar transducers have been made in a variety of configurations and shapes to make them suitable for shallow water and deep water applications, high sonic amplitude applications, and with various frequency bandpass characteristics. A problem arises in that it is often desirable to have a single transducer assembly configuration which can be utilized in a variety of applications thereby greatly reducingithe number of individual types of transducer assemblies which must be stocked for a fleet of ships. A further problem arises in that the shape of transducer elementstypically utilized in deep submergence applications has often required great dimensional stability during the curingprocess of the ceramic materials customarily utilized in such transducer elements with the result that, oftentimes, the transducer elements fail to conform to specifications so that additional ones must be provided with the attendant additional costs. Furthermore, a problem arises in that transducer assembliesproviding a limited frequency bandpass capability can only be utilized in specific applications so that other transducer assemblies must be fabricated for each new application.

SUMMARY OF THE INVENTION The foregoing problems are overcome and other advantages are provided by a sonar transducer assembly in accordance with the invention which provides for a coaxial arrangement of a front mass, a front coupling neck having a distributed impedance characteristic for matching the impedance of the front mass to other portions of the assembly, a front support ring, one or more ring shaped transducer elements arranged in an array and fabricated typically from a ceramic material such as lead zirconate-titanate having a piezoelectric characteristic or other material converting electrical energy into the mechanical energy of sonic vibrations, a rear mounting ring and a rear coupling neck which may be fabricated from a single block of metal as is done in a preferred embodiment of the invention, and a rear mass which may include a distributed mechanical impedance as is done in the preferred embodiment, all of these elements being rigidly held together by a tie rod. The tie rod passes along the transducer axis and is secured to the rear portion of the front mass and the front portion of the rear mass in a manner which provides that substantially only that portion of the tie rod between the front mass and the rear mass serves as an element in the vibrational system.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned features and other aspects of the invention are explained in the following description taken in connection with the accompanying drawing which shows, in accordance with the invention, a sectional view of a transducer assembly with the electrical connections shown schematically.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURE, there is seen a transducer assembly which, in accordance with the invention, comprises a front mass 12, a coupling neck 14, support rings 16 and 17, a ceramic assembly 18 which is seen to comprise a plurality of ceramic elements 20 each having a ring shape and being arranged coaxially, a coupling neck 22 and a rear mass 24, all of which are seen to be rigidly connected together by a tie rod 26, a nut 28 and a washer 30 and enclosed within a tubular case 32. The case 32 has two bezels 34 and 35 extending internally thereof for positioning the support rings 16 and 17. The ceramic assembly 18 is enclosed by a fiberglass wrapping 36 and has wires 38 (indicated schematically) extending from electrodes 39 positioned between the ceramic elements 20 for applying electric fields across the ceramic elements 20. The wires 38 extend to an inductor 40 which, in a wellknown manner, serves to tune the capacitance of the ceramic elements 20 for a resonance at one of the frequencies at which the transducer assembly 10 is to operate. A protective boot 42 of a watertight material, such as the commercially available product Neoprene, surrounds the case 32 and terminates at the back end of the transducer assembly 10 in a seal 44 which is vulcanized to a cable 46 through which electrical signals are coupled to the inductor 40 and the ceramic elements 20.

With, respect to the ceramic assembly 18 which serves as the transducer for converting the electrical signals of the cable 46 into sonic vibrations which radiate outwardly from the front mass, it is noted that two ceramic elements 20A-B serve as insulators to electrically insulate the electrical fields associated with the ceramic elements 20 from the support rings 16 and 17. While four of the ceramic elements 20 are shown in this embodiment of the invention, it is understood that more or less of these ceramic elements 20, even a single ceramic element 20, may serve as the transducer.

Each of these ceramic elements 20 is polarized in a direction parallel to their common axis. Each ceramic element 20, because of the relatively thick walls of these elements,is exposed to small hydrostatic stresses compared to the stresses customarily provided in the ceramicmaterial of the thin-walled tubular ceramic elements. As a result of the relatively small stresses, very favorable operation is obtained with these ceramic ring shaped elements 20. In addition, since the surfaces between adjacent ones of these ceramic elements 20 are flat, dimensional stability during the curing stage of the manufacturing process can readily be maintained to a sufficiently high degree of tolerance to permit the ceramic elements 20 to mate with each other along their adjoining surfaces.

The ceramic assembly 18 is protected from a seepage of water from outside the protective boot 42 into the interior of the case 32 by means of a seal 48 which is resilient to permit vibrational motion of the front mass 12 relative to the case 32 while preventing the seepage of water past the front mass 12.

The magnitude of the rear mass 24 and the front mass 12 and the compliance of the coupling necks l4 and 22 are selected to provide a vibratory mode wherein a node of vibration is located within the ceramic assembly 18 with the major excursions in the displacements of the various elements during vibration occurring in the axial direction within the front mass 12 and the rear mass 24. The locations of the support rings 16 and 17 correspond to points within the vibrational resonance pattern which experience only slight vibrational excursions due to their proximity to the node of vibration. Accordingly, the supportrings 16 and 17 are readily placed against the bezels 34 and 35 for positioning the vibrating elements within the case 32 since the relatively minor vibrations experienced by the support rings 16 and 17 can be isolated from the case 32 by means of vibration isolators 50 and 51 having the form of rings which are placed respectively between the support rings 16 and 17 and the bezels 34 and 35.

The transducer assembly is assembled by passing the tie rods 26 through the support ring 17, the ceramic assembly 18, the support ring 16, the coupling neck 14, and then securing the front mass 12 onto the front end of the tie rod 26 by screwing it into the threaded socket 52 of the front mass 12. The washer 30 and nut 28 are then secured forward of the back end of the tie rod 26, the nut '28 being tightened against the washer 30 and support ring 17 for prestressing the ceramic assembly 18 to maintain a positive pressure on the ceramic elements 20 under conditions of vibration. The rear mass 24 has a threaded socket 54 which is screwed onto the back end of the tie rod 26 and tightened against the coupling neck 22.

In one embodiment of the invention the inner diameter of the bezel 35 and outer diameter of the support ring 17 are less than the inner diameter of the bezel 34 so that the two masses l2 and 24 and the elements coupled therebetween can be inserted into the case 32. In an alternative embodiment the bezel 34 and the support ring 17 are supplied with keyway slots (not shown) in which case the support ring 17 is rotated slightly about its axis so that its keyway slots can pass by the keys of the keyway of the bezel 34. Or, as is shown in the figure, the case 32 may be partitioned along a threaded interface 56 in which case the front portion of the case 32 would be positioned with the support ring 16 prior to the insertion of the tie rod 26, and then would be secured onto the upper portion of the case 32 concurrently with the insertion of the rear mass 24 into the case 32. Accordingly, to complete the assembly, after joining together the front and rear masses 12 and 24 plus the elements coupled therebetween, the vibration isolators 50 and 51 are inserted adjacent their respective bezels 34 and 35. Then the rear mass 24 and the elements held thereto by the tie rod 26 are inserted and the seal 48 is applied between the case 32 and the front mass 12 to retain the support rings 16 and 17 urged lightly against their respective vibration isolators 50 and 51 and the bezels 34 and 35.

The coupling neck 14 and the rear mass 24 have distributed mechanical impedances. The coupling neck 22 and the front mass 12, due to their reduced length along their common axis, tend to have a lesser amount of distributed mechanical impedance. The impedance presented to the ceramic assembly 18 is reduced from that present at the back side of the coupling neck 14 by virtue of the relatively large area of contact between the ceramic element 20B and the back surface of the support ring 16 as compared to the cross-sectional area of the coupling neck 14, as viewed in a plane normal to the axis of the coupling neck 14. The impedance transformation provided by the coupling neck 14 enables the utilization of the ring shaped ceramic element 20 with the aforementioned axial polarization.

Each of the vibration isolators 50 and 51 may be provided with different compliances to coact with their respective support rings 16 and 17 to provide a frequency shaping of the low frequency end of the frequency bandpass characteristic of the transducer assembly 10 while the coupling necks l4 and 22 have compliances and cross-sectional areas which are selected to shape the upper frequency portion of the bandpass characteristic. Also, the differing distributed mechanical impedances of the coupling necks l4 and 22 provide a double tuned resonance characteristic to the transducer assembly 10 in which a peak response is obtained at one frequency and a second peak response is obtained at a second frequency, this first and this second frequency being selected by an appropriate choice of values of the distributed mechanical impedances.

It is also noted that the use of the threaded sockets 52 and 54 which extend through only a relatively short region of the front mass 12 and the rear mass 24 provides for a mode of vibration in the front mass 12 and V the rear mass 24 which is substantially independent of the vibrational characteristics of the tie rod 26 itself. There is also a shorter section of tie rod between the points of attachment at the front and rear masses l2 and 24 than in transducer assemblies of the prior art so that the tie rod 26 may have a more simple mode of vibration to facilitate the shaping of the frequency response characteristic of the transducer assembly 10. The masses l2 and 24, the coupling necks l4 and 22 and the support rings 16 and 17 are fabricated from a rigid, readily formable metal such as steel or aluminum. The tie rod 26 and the nut 28 may be fabricated from high strength steel.

The impedance presented to an electrical signal propagating along the cable 46 by the transducer assembly It) depends in a well-known manner upon the physical structure of the ceramic assembly 18 and the mechanical impedance presented thereto by the vibrating members, particularly the front and rear masses 12 and 24 and coupling necks l4 and 22. However, by virtue of the selection of the vibration isolators 50 and 51, and the selection of the coupling necks l4 and 22 as well as the magnitudes of the front mass 12 and rear mass 24, the impedance presented to electrical signals on the cable 46 may be made to approximate the impedance presented by transducers presently utilized in shipboard applications while retaining a broad operating band capability to permit the transducer assembly 10 to be utilized in numerous applications.

It is understood that the above-described embodiment of the invention is illustrative only and that modifications thereof will occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the embodiment disclosed herein, but it is to be limited only as defined by the appended claims.

What is claimed is:

l. A sonar transducer assembly comprising:

a front mass;

a front impedance matching means in acoustic contact with said front mass;

means for converting electrical energy into sonic energy, said converting means being coupled to said front impedance matching means;

a rear mass acoustically coupled to said converting means; said front mass, said front impedance matching means, said converting means and said rear mass being arranged along a common axis;

means positioned along said common axis and passing through said front impedance matching means and said converting means for urging together said front mass and said rear mass, said urging together means being secured to said front mass and being secured to a front portion of said rear mass to permit vibration of the remaining portion of said rear mass substantially free of a vibration of said urging together means;

a housing enclosing said front mass, said front impedance matching means, said converting means and said rear mass; said housing having a front projection and a rear projection which are inwardly directed for supporting said converting means;

a front support in contact with a front surface of said converting means and a rear support in contact with a rear surface of said converting means, said front support having an outwardly directed projection forward of and adjacent said front housing projection, and said rear support having an outwardly directed projection foward of and adjacent to said rear support;

a front and a rear ring of acoustic isolation material positioned respectively between said front ring and said front support, and said rear ring and said rear support; said rings of acoustic isolation material being positioned adjacent a node of vibration of said converting means; and

said front impedance matching means having a cylindrical shape with front and back base sections joined by a cylindrical wall, said cylindrical wall having an inner radius and an outer radius, a thickness of said cylindrical wall being less than approximately one-half the outer radius, said rear base being in acoustic contact with said converting means and having a cross-sectional area less than the cross-sectional area of said converting means,

said front base being in acoustic contact with said front mass and having a cross-sectional area larger than said rear base.

2. A transducer assembly according to claim 1 further comprising a resilient seal positioned between said front mass and said housing for resiliently holding said front mass in position relative to said housing, the compliance of the front ring of acoustic isolation material and the compliance of the rear ring of acoustic isolation material being selected to provide a frequency shaping of the frequency bandpass characteristic of said transducer assembly in cooperation with a distributed mechanical impedance of said front impedance matching means.

3. A transducer assembly according to claim 2 further comprising a rear impedance matching means positioned coaxially between said converting means and said rear mass, said rear impedance matching means having a cylindrical shape with an extension on its forward end to provide a relatively large area of contact with said converting means relative to an area of contact between said rear impedance matching means and said rear mass, said rear impedance matching means having a distributed mechanical impedance which cooperates with the distributed mechanical impedance of said front impedance matching means and the compliances of said front and said rear rings of acoustic isolation material to tune said transducer assembly. 

1. A sonar transducer assembly comprising: a front mass; a front impedance matching means in acoustic contact with said front mass; means for converting electrical energy into sonic energy, said converting means being coupled to said front impedance matching means; a rear mass acoustically coupled to said converting means; said front mass, said front impedance matching means, said converting means and said rear mass being arranged along a common axis; means positioned along said common axis and passing through said front impedance matching means and said converting means for urging together said front mass and said rear mass, said urging together means being secured to said front mass and being secured to a front portion of said rear mass to permit vibration of the remaining portion of said rear mass substantially free of a vibration of said urging together means; a housing enclosing said front mass, said front impedance matching means, said converting means and said rear mass; said housing having a front projection and a rear projection which are inwardly directed for supporting said converting means; a front support in contact with a front surface of said converting means and a rear support in contact with a rear surface of said converting means, said front support having an outwardly directed projection forward of and adjacent said front housing projection, and said rear support having an outwardly directed Projection foward of and adjacent to said rear support; a front and a rear ring of acoustic isolation material positioned respectively between said front ring and said front support, and said rear ring and said rear support; said rings of acoustic isolation material being positioned adjacent a node of vibration of said converting means; and said front impedance matching means having a cylindrical shape with front and back base sections joined by a cylindrical wall, said cylindrical wall having an inner radius and an outer radius, a thickness of said cylindrical wall being less than approximately one-half the outer radius, said rear base being in acoustic contact with said converting means and having a cross-sectional area less than the cross-sectional area of said converting means, said front base being in acoustic contact with said front mass and having a cross-sectional area larger than said rear base.
 2. A transducer assembly according to claim 1 further comprising a resilient seal positioned between said front mass and said housing for resiliently holding said front mass in position relative to said housing, the compliance of the front ring of acoustic isolation material and the compliance of the rear ring of acoustic isolation material being selected to provide a frequency shaping of the frequency bandpass characteristic of said transducer assembly in cooperation with a distributed mechanical impedance of said front impedance matching means.
 3. A transducer assembly according to claim 2 further comprising a rear impedance matching means positioned coaxially between said converting means and said rear mass, said rear impedance matching means having a cylindrical shape with an extension on its forward end to provide a relatively large area of contact with said converting means relative to an area of contact between said rear impedance matching means and said rear mass, said rear impedance matching means having a distributed mechanical impedance which cooperates with the distributed mechanical impedance of said front impedance matching means and the compliances of said front and said rear rings of acoustic isolation material to tune said transducer assembly. 